There have been known photosensitive compositions for the relief printing plates comprising various type of base resins such as a liquid unsaturated polyester, polyvinyl alcohol, a water soluble polyamide, an alcohol-soluble polyamide, a styrene copolymer, 1,2-polybutadiene and the like. The composition based on the liquid unsaturated polyester is inconvenient for handling or treating because of its liquid form. In addition, there is a problem that the composition requires the use of an alkali solution or a specified air-knife for developing.
The composition based on the polyvinyl alcohol or the water soluble polyamide has the advantage that water can be employed in developing, but it has a demerit because a water base ink can not be employed in printing because of its poor water-resistance. The composition based on cellulose acetate succinate requires use of an alkali solution and it does not have a resistance to the aqueous ink. When the base resin is the alcohol-soluble polyamide, an inflammable alcohol has to be used for developing, which is a significant defect in environmental safety. The use of the styrene-isoprene-styrene block copolymer as the base resin requires (as a developing solvent) a halogenic organic solvent, which is also a defect in environmental safety for workers.
The object of the present invention provides a photosensitive resin composition especially suitable for a relief printing plate having an excellent resistance to water based ink, whereby water or an aqueous solvent can be employed as a developing solution.